The process of manufacturing composite parts for aircraft may involve infusing a resin such as polyimide into one or more layers or plies of uncured composite reinforcement material. Heat and pressure is then applied to the resin-infused composite reinforcement material to cure and harden it, creating the desired composite part. Tubes, valves, and heat tracing elements are generally required to properly modulate the resin flow to various locations of complex-contoured composite reinforcement material. In particular, for high-temperature cures, resin lines transmitting resin to the composite reinforcement material are heat-traced to prevent the resin from cooling and solidifying in the resin line or tube. This heat-tracing adds to the cost and complexity of the process.
Another method for resin-infusing composite reinforcement material may include pleats, resin pockets, or reservoirs formed into rigid tooling or into a vacuum bag used to isolate and compress the composite reinforcement material during cure. However, the timing of when the resin is released from these pleats, pockets, or reservoirs is not controlled, so as soon as the autoclave or oven is heated to a point where the resin becomes more fluid, the resin simultaneously flows out of the various pockets or reservoirs into the composite reinforcement material. This may be acceptable for a smaller composite part receiving all of its resin from a single reservoir. But a larger part may require multiple reservoirs spaced at incremental locations along the composite reinforcement material so that each portion of the composite reinforcement material has an even amount of resin dispersed therethrough, with different reservoirs configured to saturate different zones of the composite reinforcement material with resin. If all the resin releases into the composite reinforcement material at once, air may be trapped between the multiple resin flow fronts in between adjacent zones. This trapped air may compromise the integrity of the resulting part.
Alternatively, the above-mentioned process using heat-traced tubes can include opening and closing valves to control when and how much resin is applied to different zones of the composite reinforcement material. Controlling and/or sequencing this timing of the resin application can be used to avoid trapping air between simultaneously-flowing resin flow fronts. However, as noted above, such use of tubing and valves is more expensive and complex and also requires multiple openings in the vacuum bag or mold, which could increase the risk of a bag leak. The tubing also frequently requires replacement, due to resin curing in the supply lines.